A step too far? I tried to repair a 230V Silent Night electric blanket controller (in UK). Why did I not send it back under warranty? It was still inside the 3 years! Duh! Now I am just trying to decide how it works.

Anyway it was starting to arc when switched between Low and high settings. So I took it apart and saw a bit of blackening on the sliding switch. Thought a quick repair would be to put a capacitor across the arcing terminals! Not a good idea! It finally burnt out and took out the thermal fuse!
By which time some contacts are actually black and losing their coating. So I set about tracing the circuit. I think the attached it is pretty close to schematic. It is more complex than I thought originally. I hope you can trace the two main paths for the Low (1) and High (3) switch settings? Weak point is sliding contacts with mains Live and Neutral on them!

It is amazing to me that a bunch of 1N4007 diodes are basically doing most of the work in heat control and routing current through the LED indicator. If anyone can offer a simple circuit description I am interested. It probably has a handy name like Buck dropper? Moral of the story is to send it back if under warranty or Bin it! Thermal fuses are critical in these situations and need to be exact replacements. I only had a 2A 85C to test my repair. Still didn't work. Maybe element has failed?

PS. Bought a Warmer blanket to replace. This has 2 controllers! Twice as much to go wrong, half the power though! At least the supplier has spare controllers available, unlike SilentNight.

 

Welcome to AAC!

On full power setting, the high element receives full 230VAC.
On medium setting, the high element receives half of the AC cycle because it is rectified by D1. The power delivered is more than half that of the full wave power.
On low setting, the high element receives no power while the low element receives a half-wave signal because of D2.

Bin it. The risk of being electrocuted or starting a fire is not worth it.
(or simply wire it permanently to one of the three settings, with the proper thermal fuse installed.)

 

Welcome to AAC!

On full power setting, the high element receives full 230VAC.
On medium setting, the high element receives half of the AC cycle because it is rectified by D1. The power delivered is more than half that of the full wave power.
On low setting, the high element receives no power while the low element receives a half-wave signal because of D2.

Bin it. The risk of being electrocuted or starting a fire is not worth it.
(or simply wire it permanently to one of the three settings, with the proper thermal fuse installed.)

Mr Chips thanks for the 3 obvious power paths. What confuses me is the sampling Resistor circuits and the LED circuits.

 

A step too far? I tried to repair a 230V Silent Night electric blanket controller (in UK). Why did I not send it back under warranty? It was still inside the 3 years! Duh! Now I am just trying to decide how it works.

Anyway it was starting to arc when switched between Low and high settings. So I took it apart and saw a bit of blackening on the sliding switch. Thought a quick repair would be to put a capacitor across the arcing terminals! Not a good idea! It finally burnt out and took out the thermal fuse!
By which time some contacts are actually black and losing their coating. So I set about tracing the circuit. I think the attached it is pretty close to schematic. It is more complex than I thought originally. I hope you can trace the two main paths for the Low (1) and High (3) switch settings? Weak point is sliding contacts with mains Live and Neutral on them!

It is amazing to me that a bunch of 1N4007 diodes are basically doing most of the work in heat control and routing current through the LED indicator. If anyone can offer a simple circuit description I am interested. It probably has a handy name like Buck dropper? Moral of the story is to send it back if under warranty or Bin it! Thermal fuses are critical in these situations and need to be exact replacements. I only had a 2A 85C to test my repair. Still didn't work. Maybe element has failed?

PS. Bought a Warmer blanket to replace. This has 2 controllers! Twice as much to go wrong, half the power though! AView attachment 284707View attachment 284708View attachment 284709t least the supplier has spare controllers available, unlike SilentNight.

In my experience with electric blankets in the US is i have seen the elements go to high resistance. My only guess is that when they flex back and forth enough the element resistance goes higher and higher, then eventually you only get a little heat out of one. I did have a problem with a connector one time though.
These things only seem to last so long then become problematic for some reason. Maybe a better brand name would help i dont know.

 

Note that resistor colour code gray = 8.
R1, R2, brown - gray - red - gold = 1800Ω 5%

 

Thanks. That's the colour code but I measured in circuit.

 

Thanks. That's the colour code but I measured in circuit.

If you measure in circuit you won't get the correct value, if you're getting 17K for a 1.8K resistor i would say the resistor is suspect.

 

Oops the decimal point was missing!